Singlet molecular oxygen in the form of the delta state (delta 02) has been identified as a potential atmospheric oxidant. Although ambient levels of delta 02 are not well established, we have been able to generate delta 02 at one atmosphere pressure and study its chemistry. The mean lifetime Tau was determined to be of the order of 0.1 sec and thus, it is long lived enough to react with atmospheric pollutants. We propose that delta 02 is an agent giving rises to low levels of toxic material in the atmosphere. In the hypothesis PAH adsorbed on particulate material absorb sunlight and sensitize the formation of delta 02 from proximate ground state oxygen. Delta 02 then reacts with proximate PAH on particulate surfaces forming oxygenated PAH, many of which are known to be mutagenic and/or carcinogenic. We will investigate the reaction of two PAHs, chrysene and benza[a]anthracene, adsorbed on model particulate with delta 02, and determine if PAH are self-activated (with respect to their mutagenicity) through product studies and Ames testing. The effect of light and then light and oxygen on the reaction of PAH on particle surfaces will also be studied. Product identification and Ames testing will be performed. A detailed analysis of the results will indicate the extent to which delta 02 is involved in the total chemical transformations of photooxidation reactions and whether other processes (Type I or electron transfer processes) are involved.